Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
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281.6.ASimpleServer towritedataabstractionswhichexportaspecicsetofoperationswhile notexposingtheimplementationdetailstothecaller.Therearesomedifferences:<br />
<strong>Hermes</strong>processesareactive.Iftherearemultiplecallers,thecalls arequeued<strong>and</strong>processedserially.Theprocesscanchoosenotto<br />
Icontrolaccessin<strong>Hermes</strong>onaport-by-portbasis.InAdaorin Icanwritedierent<strong>Hermes</strong>processeswiththesameinterface<strong>and</strong> ofthesameprivatetypewiththesamespecication(interface)<strong>and</strong> receivecertaincallsatcertaintimes.Thereisnoneedformonitors dierentprivateparts. orsemaphoresorothermutualexclusionmechanisms.<br />
callGetLinecouldalsocallPutLine<strong>and</strong>Quit.Thisisundesirable, accesstoanobjectautomaticallygivesaccesstoallitsoperations.In thecaseofaboundedbuer,thiswouldmeanthatanyonewhocould object-orientedlanguages,Icontrolaccessonanobjectbasis.Having dierentinternals.InAda,forinstance,Ican'thavetwovariables<br />
totallyordered|thatis,eachelementhasanassociatedposition.Positions thetable,thelastpositionisk1. anorderedtable.Atableissimplyacollectionofvaluesofthesametype aredenotedbyintegers.Therstpositionis0.Iftherearekelementsin (mathematically,abag).Anorderedtableisatablewhoseelementsare TheQueueisanexampleofatypefamilywehaven'tstudiedbefore| <strong>and</strong>infactIdon'twantthereaders<strong>and</strong>writersoftheboundedbuer<br />
Youhavealreadyusedorderedtableswithoutknowingit,sincethepredenedtypeCharstringisanorderedtableofelementsoftypeChar.<br />
toevenhavetoknowthattheQuitoperationexists.<br />
whichisatablewhoseelementsareoftypeT.Inourexample,wewant todeneatypeLinesasanorderedtablewhoseelementsareoftype initionsmoduleBBLocal: Charstring.Thetypedenitionlookslikethis<strong>and</strong>willappearinthedef-<br />
In<strong>Hermes</strong>youc<strong>and</strong>enetablesofanytype|tablesofintegers,tablesof callmessages,etc.Youcanevendenearecursivetabletype|atypeT<br />
fromthetablehavetypestateinit.Noticethatlikeothertypedenitions tablewithaparticularcontent,insertelementsintothetable,removeelementsfromthetable,mergeonetableintoanother,extractorcopyouta<br />
in<strong>Hermes</strong>,<strong>and</strong>unliketypedenitionsinmanyotherlanguages,tabletype aCharstring,<strong>and</strong>thatelementsinsertedinto,removedfrom,orcopied le),<strong>and</strong>nothingabouthowmuchstoragetoallocate. denitionssaynothingabouttherepresentation(e.g.array,linked-list,disk ThedenitionsaysthatLinesisanorderedtable,thateachelementis Lines:orderedtableofCharstringfinitg; Alltablessupportthefollowingoperations:inspectanelementinthe
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